Light emitting diodes (LEDs) are solid state devices that convert electric energy to light, and generally include one or more active layers of semiconductor material sandwiched between oppositely doped layers. When bias is applied across doped layers, holes and electrons are injected into one or more active layers where they recombine to generate light that is emitted from the device. Laser diodes are solid state emitters that operate according to similar principles.
Solid state light sources may be utilized to provide white light (e.g., perceived as being white or near-white), and have been investigated as potential replacements for conventional white incandescent and/or fluorescent lamps. Light perceived as white or near-white may be generated by a combination of red, green, and blue (“RGB”) emitters, or, alternatively, by combined emissions of a blue light emitting diode (“LED”) and a yellow phosphor. In the latter case, a portion of the blue LED emissions pass through the phosphor, while another portion of the blue LED emissions is ‘downconverted’ to yellow; the combination of blue and yellow light provide a white light. Another approach for producing white light is to stimulate phosphors or dyes of multiple colors with a violet or ultraviolet LED source.
Many modern lighting applications require high power solid state emitters to provide a desired level of brightness. High power solid state emitters can draw large currents, thereby generating significant amounts of heat that must be dissipated. Many solid state lighting systems utilize heatsinks in thermal communication with heat-generating solid state light sources. For heatsinks of substantial size and/or subject to exposure to a surrounding environment, aluminum is commonly employed as a heatsink material, owing to its reasonable cost, corrosion resistance, and relative ease of fabrication. Aluminum heatsinks for solid state lighting devices may be formed in various shapes by techniques such as casting, extrusion, and/or machining.
Elongated lighting devices such as fluorescent tube-based light fixtures are widely employed in commercial and industrial buildings, as well as in some residential environments. Solid state lighting devices are capable of operating at much greater luminous efficiency and greater reliability than fluorescent tubes, but solid state lighting devices generally include small-area emitters that approximate point sources—in contrast to the large emissive area characteristic of fluorescent tubes. It would be desirable to provide solid state lighting devices similar in size and conformation to fluorescent tube-based devices to enable retrofit of solid state light bulbs or solid state light fixtures in the same or a comparable envelope of space.
Certain elongated solid state lighting devices have been disclosed in the art. U.S. Patent Application Publication No. 2008/0037257 to Bolta (“Bolta”) discloses a LED light fixture including at least one elongated heat transfer mounting bar, at least one emitter plate secured to the mounting bar, an array of LEDs secured to each emitter plate, and a diffusion lens arranged over the LED array. Mounting bars and/or heatsink portions thereof, which may be formed by extrusion, may be arranged in parallel to define air channels therebetween. Exterior and/or interior fans may be used to promote convective cooling. Another elongated device for focusing LED light on an illumination area is disclosed in U.S. Pat. No. 6,871,993, with the elongated device including multiple elongated fins arranged in parallel defining channels therebetween.
Elongated solid state lighting devices known in the art suffer from various limitations that restrict their utility. Elongated fins arranged parallel to one another tends to reduce the effectiveness of cross-flow air cooling (since channels between fins may be sheltered by adjacent fins), and can cause undesirable directional stratification of temperature over the length of an elongated lighting device when exposed to a parallel air flow (since the temperature of air flowing parallel to elongated inter-fin cooling channels increases as air travels from a leading edge of one channel to the trailing edge thereof). Directional stratification of temperature over the length of an elongated lighting device may be exacerbated when parallel fins extend in a downward or generally sideward direction, since natural convection may tend to trap heat in elongated inter-fin cooling channels.
It also may be cumbersome to mount and route electrical connections (e.g., conductors) to numerous solid state emitters arranged in one or more recesses and/or nonplanar surfaces of a conventional elongated solid state lighting device. Complex heatsink shapes may be expensive to form by extrusion or casting, and heatsinks formed by casting may be characterized by lower density than shapes formed by other techniques, with concomitant reduction of thermal conduction capability (which may require larger heatsinks to be used). Manufacturing difficulty and component expense are non-trivial, since the high cost of solid state lighting devices has impaired their widespread adoption.
It may also be difficult to place heat transfer structures in or on lighting devices while providing wide-angle light output without undue shadowing, particularly in view of the point source character of conventional solid state light emitters.
It would be desirable to provide elongated solid state lighting devices capable of reducing some or all of the limitations inherent to conventional elongated lighting devices.